One problem associated with using photographic apparatuses such as cameras is that, on the one hand, the user wants to minimize the amount of excessive light entering the camera through the lens, also called stray light, and on the other hand, the user wants to obtain clear, crisp and sharp pictures by letting a sufficient amount of light entering the camera as described. One way of cutting down the stray light known in the art is by utilizing an extendable lens hood. This hood screens off superfluous light entering the lens from other directions than directly from the intended subject for the picture to be taken. To accommodate for different focal length lenses, the hood is arranged as a bellows, or similar extendable device, having a first end attached to the lens and a second end open towards the subject. The length of the bellows can be changed by sliding the second end of the hood on a saddle. The user has to have some indication as to how far the hood can be slid forward for any given lens, without cutting of the corners or the sides of the picture projected on the film frame by being slid forwards too far. This can be accomplished by supplying an engraved or otherwise marked scale on the saddle, indicating allowable positions for the second end of the hood for any given lens. One drawback with the above lens hood is that the scale will be very complicated because the optimal setting of the lens hood not only varies with what lens is used, but also with what opening is set of the diaphragm of the lens and the actual focusing distance used. A smaller opening permits a further extension of the hood than a larger opening and a close focusing distance also permits a further extension of the hood than a focusing distance closer to infinity, i.e. far away subjects. Thus, to take all possible settings for all possible lenses into account will result in a scale having a large number of markings. Such a scale is practically impossible to produce. As an alternative, every lens could have its own lens hood with a scale pertaining only to that lens and having markings for different openings correlated to different focusing distances. Also this type of solution has drawbacks, the cost for the user being one, because the user would have to purchase several extendable lens hoods, one for each lens.
An alternative is for the user to memorize, through experience, which extension length of the hood works best with which lens. This is probably a big drawback for most users who want to be able to use their camera without complicated, expensive and lengthy initial trial periods.